In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, a transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message in a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 10, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of the channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has also been a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 11(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 11(b), or, as shown in FIG. 11(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIG. 11.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
As shown in FIG. 12, in the Enhanced Uplink, the mobile station UE is configured to give the highest priority to a “Down” command, when a relative transmission rate control channel (RGCH: Relative rate Grant Channel) received from a non-serving cell includes a “Down” command even while a relative transmission rate control channel (RGCH) received from a serving cell includes an “Up” command (refer to Non-patent Document 1).
Here, the non-serving cell is configured to determine, based on the state of the interference power in the non-serving cell, whether or not to transmit a relative transmission rate control channel (RGCH) including a “Down” command (refer to Non-patent Document 2).
However, in a conventional transmission rate control method, a relative transmission rate control channel (RGCH) including a “Down” command can be transmitted in consecutive time intervals, and thereby, QoS expected by the serving cell cannot be satisfied. This leads to a problem that service quality may be deteriorated.    Non-patent Document 1: 3GPP TSG-RAN TS25.309 v6.2.0    Non-patent Document 2: 3GPP TSG-RAN R2-05907